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FFT - Rohde & Schwarz RTB2002 vs. Siglent SDS2104X Plus
Andreas:
--- Quote from: Hardware on September 18, 2020, 08:55:24 pm ---
What surprises me is that the siglent shows more peaks than the R&S.
--- End quote ---
The R&S simply seems to clip the curves near the noise floor of -60 dbm .
The Siglent shows much lower amplitudes too. (how many points does the FFT have on each device?)
with best regards
Andreas
maginnovision:
You should probably turn off 10bits mode on the siglent. Also is avg=4 averaging the waveform or avg of 4 ffts. The waveform should ideally fill the display as well. I'd also do standard sample over high res on R&S to be able to get more like for like comparison.
Hardware:
Unfortunately I can't answer the question about the points anymore, because the R&S oscilloscope is on its way back. In the specifications of R&S I can't find any statement about the number of points per second at the moment.
Andreas:
Hello,
to get a RBW of 33 Hz I have to use a insane low number of FFT points.
At 8 kPts I also do not see any further harmonics.
with 1 MPts the bandwidth or in my case bin width decreases
so also the noise floor goes down making the harmonics visible.
Increasing the ADC resolution to 16 Bits further decreases the noise floor.
And there are other tricks like averaging several FFTs possible.
with best regards
Andreas
2N3055:
--- Quote from: Hardware on September 18, 2020, 08:55:24 pm ---The display may be a bit confused now. In the first case I compare the FFT of the sine 1kHz of the siglent with the FFT of the sine 1kHz of the R&S.
In the second case I compare the FFT of the rectangle 100kHz of the siglent with the FFT of the rectangle 100kHz of the R&S. The SPAN range between the 1kHz (0-6kHz) and the 100kHz signal (0-600kHz) is different.
What surprises me is that the siglent shows more peaks than the R&S.
In my opinion the siglent shows too many peaks. Unfortunately I cannot check it with a real spectrum analyzer because I don't have one.
But the SGS2042X has so many that I am sure there is someone who has a spectrum analyzer and can show a photo.
I am interested in which oscilloscope is better or more correct.
--- End quote ---
You didn't compare FFT at same settings. like I said before.
Siglent display shows much lower noise floor and has much better RBW. We also don't know if same windowing function was used.
Peaks visible on Siglent are buried in noise on R&S.
Looking at this Siglent looks better by a mile. Actually I think that with proper settings R&S should do better... FFT is quite complicated sometimes and need some time to get acquainted with how it's implemented on particular scope.
I just saw Andreas already said most of this..
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